JPH05135399A - Optical head - Google Patents

Abstract

PURPOSE:To miniaturize the constitution and to make the cost low by constituting a beam shaping prism with a reflection type and a transmission type beam shaping prisms having the same incident planes and the same light-emitting surfaces, making an angle between an incident optical axis and a light-emitting optical axis a right angle and selecting an optical constant so as to cancel and correct a color aberration each other. CONSTITUTION:A luminous flux 2 outgoing from a semiconductor laser element 1 is made a parallel luminous flux 4 by a collimate lens 3 and incident on the incident plane 13a of the first reflection type beam shaping prism 13. The luminous flux 15 refracted on the surface 13a is reflected from the reflection surface 13b and becomes the luminous fluxes 16, 17 and refracted on the incident plane 14a of a second transmission type beam shaping prism 14 and becomes the luminous fluxes 18, 19 and is emitted from the light-emitting surface 14b. The angle between the optical axis 4a of the luminous flux 4 and the optical axis 19a of the luminous flux 19 is made 90 degree and the optical constant is set so as to cancel the color aberration by the fluctuation of the wavelength of the prisms 13, 14 and to correct it. Thus, the luminous flux is deflected 90 degree without using a reflection mirror, etc., and an optical head is miniaturized and made a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a beam shaping prism for converting the anisotropy of laser light into an isotropic one, and is mounted on a device depending on the size of an optical head. Due to the limitation, in an optical head that requires the optical path from the semiconductor laser to the light separating means to be deflected by 90 degrees using a reflection mirror or the like, without particularly providing the deflection means such as the reflection mirror. The present invention relates to an optical head suitable for mounting in which a beam shaping prism for converting anisotropy of laser light into isotropicity is constituted so that an incident optical axis and a reflected optical axis form 90 degrees.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional optical head using two conventional transmission type beam shaping prisms as a beam shaping prism and a reflection mirror for deflecting an optical path by 90 degrees. Is.

An anisotropic divergent light beam 2 emitted from a semiconductor laser element 1 which is a linearly polarized light source becomes a parallel light beam 4 by a collimator lens 3. The parallel light flux 4 becomes refracted light 52 because the incident surface 50a of the beam shaping prism 50 is oblique to the optical axis 4a of the light flux 4.
The refracted light 52 is emitted from the exit surface 50b of the beam shaping prism 50.
The light beam 53 is transmitted without being refracted by. Luminous flux 5
3 enters a beam shaping prism 51 having the same shape as the beam shaping prism 50. Here, the luminous flux 53 is
The incident surface 51a of the beam shaping prism 51 is formed obliquely with respect to the optical axis 53a of the light beam 53.
Becomes The refracted light 54 becomes a light beam 55 that is transmitted without being refracted by the emission surface 51b of the beam shaping prism 51. As described above, the incident light beam 4 is shaped into the outgoing light beam 55 having vertical and horizontal isotropic properties by being refracted twice in the process of passing through the transmissive beam shaping prisms 50 and 51. Also the luminous flux 4
Angle of incidence on the incident surface 50a of the
By making the incident angles with respect to 1a equal, the emitted light 55 becomes parallel to the optical axis 4a of the incident light 4. When mounting the optical head on the apparatus, if the semiconductor laser 1, the collimator lens 3, the beam shaping prisms 50 and 51, and the beam splitter 6 are aligned in the A direction, the optical path length becomes long. Become. That is, due to the restriction of the length of the optical head in the A direction, it is necessary to shorten the length in the A direction by deflecting the optical path from the semiconductor laser element 1 to the beam splitter 6 as the light separating means by 90 degrees. .. Therefore, in the conventional optical head shown in the figure, the beam-shaped light beam 55 is deflected by 90 degrees in the optical path by using the mirror 56. The light beam 5 reflected by the mirror 56 passes through the beam splitter 6 and is reflected by the mirror 7. After that, the parallel light flux 5 is condensed by the objective lens 8 and irradiated onto the information recording surface 9a of the disc 9 which is an optical information recording medium.

The reflected light beam 10 from the disk 9 is converted into a parallel light beam 11 again by the objective lens 8 and is reflected by the mirror 7 and then further reflected by the reflecting surface 6 of the beam splitter 6.
reflected by a. The reflected parallel light flux 12 is guided to the detection optical system 100 and detected as a servo signal for positioning a focused spot on the information recording surface 9a of the disk 9 and an information signal.

[0005]

However, in the optical head using the above-mentioned conventional transmission type beam shaping prisms 50 and 51, the semiconductor laser 1, the collimating lens 3, the beam shaping prism 50 and the beam are used. -Since the beam splitter 6 is arranged linearly, it is not considered that the distance from the semiconductor laser 1 to the beam splitter 6 (direction A) becomes long and the optical head becomes large. There is a problem in that the optical head is mounted on the device. Further, in order to shorten the distance in the A direction, a component such as a mirror is provided in the optical path from the semiconductor laser device 1 to the beam splitter 6, and the optical axis is deflected by 90 degrees, apparently in the A direction. Although it is possible to shorten the distance, there is a problem that the number of parts is increased because it is necessary to provide new parts. On the other hand, if one beam shaping prism 50 is used and the beam shaping is performed, the optical path length can be shortened. However, in this case, there is a problem that the optical axes of the incident light and the outgoing light with respect to the beam shaping prism are bent and the structure of the optical head becomes complicated, and the wavelength variation of the laser light of the semiconductor laser element 1 is caused. If it occurs, there is a problem that the optical axis tilt of the light emitted from the beam shaping prism is changed, and the optical performance of the optical head is deteriorated.

An object of the present invention is to provide an optical head capable of deflecting the optical path from the semiconductor laser element 1 to the beam splitter 6 by 90 degrees without increasing the number of parts of the optical head. ..

[0007]

In order to achieve the above object, the beam shaping prism includes a reflection type beam shaping prism having an incident surface and an emission surface which are the same, and a transmission type. A beam shaping prism, and an incident angle .theta.1 of the incident light beam on the incident surface of the reflection type beam shaping prism, and an incidence surface of the reflection type beam shaping prism and the transmission type beam shaping prism. The relationship between the relative angle γ with respect to the surface, the relative angle β between the entrance surface and the exit surface of the transmissive beam shaping prism, and the refraction angle θ9 of the outgoing light flux at the exit surface of the transmissive beam shaping prism. This is achieved by devising and arranging the shapes of the reflective beam shaping prism and the transmission beam shaping prism so as to satisfy the following equation (1).

[0008]

[Equation 1]

[0009]

The operation will be described with reference to FIG. The anisotropic parallel light flux 100 emitted from the semiconductor laser element 1 is a reflection type beam shaping prism 13 (refractive index N1) which is the first beam shaping prism of the beam shaping prism. Is incident from the incident surface 13a. Here, the incident light 100 is the incident surface 1
Since 3a is oblique to the incident optical axis 100a (incident angle θ1), it is refracted (refraction angle θ2). Then, the refracted light flux 101 is reflected (reflection angle θ3) by the reflecting surface 13b inclined (relative angle α) with respect to the incident surface 13a, and then the reflected light 102 is incident on the same surface 13c as the incident surface 13a (incident). Then, the light is refracted (refraction angle θ5) and emitted. The incident surface 14 of the transmission type beam shaping prism 14 (refractive index N2) which is the second beam shaping prism.
It is incident on a. Here, the incident light beam 103 is incident on the transmissive beam shaping prism in which the incident surface 14a is inclined (relative angle γ) with respect to the incident surface 13a (emission surface 13c) of the reflective beam shaping prism. Here, the incident surface 14a is the incident optical axis 1
It is refracted (refraction angle θ7) because it is oblique (incident angle θ6) with respect to 03a. And the refracted light beam 10
The light beam 4 enters the exit surface 14b that is inclined (relative angle β) with respect to the entrance surface 14a (incident angle θ8), is refracted (refraction angle θ9), and exits. Therefore, the following relational expression holds.

[0010]

[Equation 2]

[0011]

[Equation 3]

[0012]

[Equation 4]

[0013]

[Equation 5]

[0014]

[Equation 6]

[0015]

[Equation 7]

[0016]

[Equation 8]

As described above, the anisotropic parallel light beam 100 emitted from the semiconductor laser device 1 is incident on the incident surface 1 of the reflection type beam shaping prism 13 which is the first beam shaping prism.
3a and the exit surface 13c are refracted by the entrance surface 14a and the exit surface 14b of the transmissive beam shaping prism 14 which is the second beam shaping prism, so that the beam is enlarged in the direction parallel to the paper surface. To be done. That is, assuming that the beam diameter of the incident light 100 is a and that of the emitted light 105 is b, the beam shaping ratio is expressed by the following equation.

[0018]

[Equation 9]

Further, the incident angle θ1 of the incident light 100 on the incident surface 13a of the reflection type beam shaping prism 13 and the incident surface 13a of the reflection type beam shaping prism 13 and the transmission type beam shaping prism 14. The relative angle γ with respect to the incident surface 14a, and the incident surface 14a and the outgoing surface 14b of the transmissive beam shaping prism 14.
And the relative angle β with respect to the refraction angle θ9 of the outgoing beam 105 at the exit surface 14b of the transmissive beam shaping prism 14
The reflective beam shaping prism and the transmissive beam shaping prism are devised and arranged so as to satisfy the above condition, so that the angle formed by the incident light 100 and the outgoing light 105 is 90.
It is possible to set the degree, without using a mirror etc.
The optical path from the semiconductor laser element 1 to the beam splitter 6 which is the light separating means can be deflected by 90 degrees.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical head of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the optical head of the present invention.

In FIG. 1, a light beam 2 emitted from a semiconductor laser device 1 which is a linearly polarized light source and which is a divergent light whose intensity is anisotropic is made into a parallel light beam 4 by a collimator lens 3, and the present invention is used. The first beam shaping prism of the second beam shaping prism is incident on the incident surface 13a of the reflection type beam shaping prism 13. Here, the incident light flux is refracted because the incident surface 13a is oblique to the incident optical axis 4a. Then, the refracted light beam 15 is reflected by the reflecting surface 13b of the reflective beam shaping prism 13. Reflected light beam 16
Exits from the same surface 13c as the incident surface 13a again. Then, it is incident on the incident surface 14a of the transmission type beam shaping prism 14 which is the second beam shaping prism. Here, the incident light beam 17 is refracted because the incident surface 14a is oblique to the incident optical axis 17a. Then, the refracted light beam 18 is emitted from the exit surface 14b of the transmissive beam shaping prism 14.
Emit more. The anisotropic laser light 4 is reflected by the reflective beam.
The incident surface 13a of the beam shaping prism 13 and the incident surface 14a of the transmissive beam shaping prism 14 are shaped into an optical beam 19 having vertical and horizontal isotropic properties.
In the present embodiment, for the sake of simplicity, the outgoing light 17 exiting the reflective beam shaping prism 13 and the outgoing light 13c are perpendicular to the outgoing surface 13c and exit light 19 exiting the transmissive beam shaping prism 14. The emission surface 14b is also vertical. As a result, the beam shaping ratio m of the beam shaping prism of this embodiment is given by the following equation.

[0023]

[Equation 10]

Further, the conditional expression for making the incident light 4 and the outgoing light 19 perpendicular to each other is such that, when the refraction angle θ9 = 0 at the exit surface 14b of the transmissive beam shaping prism 14 of the light beam 18 in the equation 1, Incident surface 1 of the reflective beam shaping prism 13 of
Angle of incidence θ1 on 3a and reflective beam shaping prism 13
Relative angle γ between the incident surface 13a of the transparent beam shaping prism 14 and the incident surface 14a of the transmissive beam shaping prism 14 and the transmissive beam shaping prism 1
4 and the relative angle β between the incident surface 14a and the exit surface 14b are given by the following equation.

[0025]

[Equation 11]

By devising the shapes of the reflection type beam shaping prism 13 and the transmission type beam shaping prism 14 so as to satisfy the above expression, the incident light beam 4 incident on the reflection type beam shaping prism 13 is made. The angle between the incident optical axis 4a and the optical axis 19a of the light beam 19 emitted from the transmissive beam shaping prism 14 can be set to 90 degrees. Therefore, like the conventional head, even if an optical component such as a mirror is newly provided in the optical path and the optical path is not deflected by 90 degrees, the optical path can be deflected by 90 degrees only by the beam shaping prism. The light beam 19 emitted from the transmissive beam shaping prism 14 passes through the beam splitter 6 composed of two triangular prisms 6a and 6b and is reflected by the mirror 7. After that, the parallel light flux 19 is
The light is condensed by the objective lens 8 and irradiated onto the information recording surface 9a of the disc 9 which is an optical information recording medium.

The reflected light beam 10 from the disk 9 is converted into a parallel light beam 11 by the objective lens 8 again, is reflected by the mirror 7, and is further reflected by the reflecting surface 6 of the beam splitter 6.
reflected by c. The parallel light flux 12 after reflection is guided to the detection optical system 100, and the information recording surface 9 a of the disc 9 is recorded.
A servo signal for positioning the focused spot on the upper side and an information signal are detected. Since the servo signal and the information signal are essentially unrelated to the present invention, detailed description thereof will be omitted.

Next, used in the optical head of this embodiment,
A specific design example of the beam shaping prisms 13 and 14 will be described.

When the glass material of the reflection type beam shaping prism 13 and the transmission type beam shaping prism is BK-7 and the beam shaping ratio is 3, the calculation is as follows. N1 = N2 = 1.51, m = 3, α = 18.6
°, β = 34.4 °, γ = 58.5 °, θ1 = 65.9
°, θ6 = 58.5 ° On the other hand, the above design value satisfies the conditional expression given by the equation 11 in which the incident light and the outgoing light are vertical. Therefore, the beam shaping prism of the present embodiment (reflection type beam shaping prism 13
And a transmissive beam shaping prism 14) can be used to shape the anisotropy of the laser light, and at the same time the optical path can be deflected by 90 degrees without newly providing an optical component such as a mirror in the optical path. .. As a result, the optical head can be downsized, which is advantageous in mounting the optical head on the apparatus.

On the other hand, the laser light 2 emitted from the semiconductor laser device 1 has a wavelength variation due to temperature variation and the like. This wavelength variation causes variation in the magnification of the beam shaping prism and variation in the optical axis tilt of the emitted light 19 to cause deterioration of the optical performance of the optical head. Therefore, even if the wavelength variation occurs, it is necessary to correct the variation of the magnification of the beam shaping prism and the variation of the inclination of the optical axis of the emitted light 19. The correction conditions in this embodiment are as follows.

[0031]

[Equation 12]

A design example of a beam shaping prism with chromatic aberration corrected will be described below.

BK-7 is used as the glass material of the reflection type beam shaping prism 13 and the transmission type beam shaping prism, and calculation is performed for the case where the beam shaping ratio is 3.2. ..

N1 = N2 = 1.51, m = 3.2, α =
18.27 °, β = 36.54 °, γ = 63.27 °,
[theta] 1 = 63.27 [deg.], [theta] 6 = 63.27 [deg.] On the other hand, the above design values satisfy the conditional expression given by the equation 11 in which the incident light and the outgoing light are vertical. Therefore, the beam shaping prism of the present embodiment (reflection type beam shaping prism 13
And a transmissive beam shaping prism 14) can be used to shape the anisotropy of the laser light, and at the same time the optical path can be deflected by 90 degrees without newly providing an optical component such as a mirror in the optical path. .. Further, it becomes possible to correct chromatic aberration due to wavelength fluctuation of the laser light 2 emitted from the semiconductor laser element 1. As a result, the size of the optical head can be reduced without deteriorating the performance of the optical head, which is advantageous for mounting on an apparatus.

Next, the second embodiment of the present invention will be described with reference to FIG.
Will be explained. 3, the same symbols as in FIG. 1 indicate the same parts.

The beam shaping prism of the present embodiment is obtained by reversing the positional relationship between the reflection type beam shaping prism 13 and the transmission type beam shaping prism 14 of the first embodiment. That is, the parallel light beam 4 emitted from the collimating lens 3 is
First, the beam is transmitted through the transmissive beam shaping prism 14 and then reflected by the reflective beam shaping prism 13 to obtain a beam.
Shaping is performed. The description is omitted because it is the same as that of the first embodiment until it passes through the reflection type beam shaping prism 13, is irradiated onto the disk 9, and is guided to the detection optical system 100.

As described above, if the beam shaping prism of this embodiment (the reflection type beam shaping prism 13 and the transmission type beam shaping prism 14) is used, the anisotropy of the laser light can be shaped. At the same time, the optical path can be deflected by 90 degrees without newly providing an optical component such as a mirror in the optical path. As a result, the optical head can be downsized, which is advantageous in mounting the optical head on the apparatus. In addition,
It is also possible to correct chromatic aberration due to wavelength fluctuation of the element 1.

Next, a third embodiment of the present invention will be described with reference to FIG.
Will be explained. 4, the same symbols as in FIG. 1 indicate the same parts.

The beam shaping prism of this embodiment is a combination of the transmission type beam shaping prism 14 of the first embodiment and the beam splitter 6. That is, the first and second
In place of one triangular prism 6a of the beam splitter 6 of the embodiment, an incident surface 25d is a triangular prism 25a having an inclination with respect to the incident optical axis 17a. This inclination angle β is made equal to the inclination angle β of the transmissive beam shaping prism of the first embodiment. As a result, the incident optical axis 4a of the light beam 4 entering the reflection type beam shaping prism 13 and the beam splitter 25.
The angle formed by the optical axis 26a of the luminous flux 26 that emits is 90 degrees. It passes through the beam splitter 25, irradiates the disk 9 and is guided to the detection optical system 100 until the first
The description is omitted because it is the same as the embodiment described above.

As described above, the reflection type beam shaping prism 13 of this embodiment and the beam splitter 25 having a beam shaping function.
By using (1), it is possible to shape the anisotropy of the laser light and reduce the optical path by 90 degrees without newly providing an optical part such as a mirror in the optical path as well as reducing the number of optical parts.
As a result, the optical head can be downsized, which is advantageous in mounting the optical head on the apparatus. Further, it is possible to correct chromatic aberration due to the wavelength variation of the laser element 1.

As described in detail above, the beam of the present invention is
If the beam shaping prism is used, it is possible to correct the anisotropy of the semiconductor laser, reduce the size of the optical system, and correct the deviation of the optical axis of the emitted light due to the wavelength variation.

[0042]

By using the beam shaping prism of the present invention, the anisotropy of laser light can be shaped and a new mirror can be formed.
It is possible to deflect the optical path by 90 degrees without providing optical components such as the above in the optical path, and at the same time, it is possible to correct chromatic aberration due to wavelength fluctuation of the laser element 1. As a result, the optical head can be downsized, which is advantageous in mounting the optical head on the apparatus.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical head according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a beam shaping prism used in the optical head of the present invention.

FIG. 3 is a configuration diagram of an optical head according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical head according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical head using a conventional beam shaping prism.

[Explanation of Codes] 1 ... Semiconductor laser element, 3 ... Collimating lens, 9 ... Disk, 13, 14 ... Beam shaping prism, 6, 25 ...
Beam splitter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akira Saito Akira Saito 2880 Kokufu, Odawara, Kanagawa Hitachi Ltd. Odawara factory (72) Inventor Yasuo Kitada 2880 Kokufu, Odawara, Kanagawa Hitachi Ltd. Odawara factory

Claims (5)

[Claims] 1. A semiconductor laser device, a collimating lens for converting divergent light emitted from the semiconductor laser device into parallel light, and anisotropy of the laser. Beam shaping prism, an objective lens for condensing the laser to guide it onto an information recording surface of an optical information recording medium, and an optical system for detecting a reflected light beam or a transmitted light beam from the information recording surface. In the optical head, the beam shaping prism is composed of a first beam shaping prism and a second beam shaping prism, and the first beam shaping prism is provided. The beam shaping prism is a reflection type beam shaping prism having an entrance surface and an exit surface and having a reflecting surface.
An optical head characterized in that the beam shaping prism is a transmissive beam shaping prism having an entrance surface and an exit surface. 2. An angle formed by an incident optical axis of the first beam shaping prism and an outgoing optical axis of the second beam shaping prism of the beam shaping prism is 90 degrees. The optical head according to claim 1, wherein: 3. The optical head according to claim 1 or 2, wherein a beam shaping function of the transmissive beam shaping prism is added to the light separating means. 4. A variation in the inclination of the optical axis of the laser light emitted from the beam shaping prism, which occurs with the wavelength variation of the laser light emitted from the semiconductor laser element, is corrected. 2. The reflection type beam shaping prism and the transmission type beam shaping prism are set as described above.
4. The optical head according to claim 3. 5. An incident angle .theta. Of the laser beam on the incident surface of the reflection type beam shaping prism.
1, the relative angle γ between the incident surface of the reflective beam shaping prism and the incident surface of the transmissive beam shaping prism, and the relative angle between the incident surface and the outgoing surface of the reflective beam shaping prism. The reflection-type beam shaping prism and the transmission-type beam shaping prism are set so that the relationship of α satisfies sin (γ)-(cos (γ) / cos (2α)) × sin (θ1) = 0. The optical head according to any one of claims 1 to 4, wherein: